Java GUI Components: Details         

Swing Overview JLabel Event Handling Model JTextField and JPasswordField JTextArea JButton JCheckBox JComboBox

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Mouse Event Handling Layout Managers   

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Panels 

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FlowLayout BorderLayout GridLayout Creating a Self-Contained Subclass of JPanel

Windows Using Menus with Frames 19

Swing Overview 

Swing GUI components  Defined in package javax.swing  Original GUI components from Abstract Windowing Toolkit in java.awt  Heavyweight components - rely on local platform's windowing system for look and feel  Swing components are lightweight  Written in Java, not weighed down by complex GUI capabilities of platform  More portable than heavyweight components  Swing components allow programmer to specify look and feel  Can change depending on platform  Can be the same across all platforms 20

Swing Overview java.lang.Object java.awt.Component java.awt.Container javax.swing.JComponent

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Swing Overview 

Swing component inheritance hierarchy  Component defines methods that can be used in its subclasses  Container - collection of related components  

When using JFrames, attach components to the content panel (a Container) Method add to add components to content pane

 JComponent

-

superclass

to

most

Swing

components  Much of a component's functionality inherited from these classes

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JLabel  Labels    

Provide text instructions on a GUI Read-only text Programs rarely change a label's contents Class JLabel (subclass of JComponent)

 Methods  

Can declare label text in constructor myLabel.setToolTipText( "Text"

 Displays "Text"in a tool tip when mouse over label  

myLabel.setText( "Text" ) myLabel.getText() 23

Event Handling Model 

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GUIs are event driven  Generate events when user interacts with GUI  Mouse movements, mouse clicks, typing in a text field, etc.  Event information stored in object that extends AWTEvent To process an event  Register an event listener  Object from a class that implements an event-listener interface (from java.awt.event or javax.swing.event)  "Listens" for events  Implement event handler  Method that is called in response to an event  Each event handling interface has one or more event handling methods that must be defined

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Event Handling Model 

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Delegation event model  Use of event listeners in event handling  Processing of event delegated to particular object When an event occurs  GUI component notifies its listeners  Calls listener's event handling method Example:  Enter pressed in a JTextField  Method actionPerformed called for registered listener

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TextField and JPasswordField 

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JTextFields and JPasswordFields  Single line areas in which text can be entered or displayed  JPasswordFields show inputted text as *  JTextField extends JTextComponent  JPasswordField extends JTextField When Enter pressed  ActionEvent occurs  Currently active field "has the focus" Methods  Constructor  JTextField( 10 ) - sets textfield with 10 columns of text  JTextField( "Hi" ) - sets text, width determined automatically 26

JTextField and JPasswordField 

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Methods (continued)  setEditable( boolean )  If true, user can edit text  getPassword  Class JPasswordField  Returns password as an array of type char Example  Create JTextFields and a JPasswordField  Create and register an event handler  Displays a dialog box when Enter pressed 27

JTextArea 

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Area for manipulating multiple lines of text  Like JTextField, inherits from JTextComponent  Many of the same methods JScrollPane  Provides scrolling  Initialize with component  new JScrollPane( myComponent )  Can set scrolling policies (always, as needed, never) Box container  Uses BoxLayout layout manager  Arrange GUI components horizontally or vertically  Box b = Box.createHorizontalbox();  Arranges components attached to it from left to right, in order attached 28

JButton 

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Button  Component user clicks to trigger an action  Several types of buttons  Command buttons, toggle buttons, check boxes, radio buttons Command button  Generates ActionEvent when clicked  Created with class JButton  Inherits from class AbstractButton Jbutton  Text on face called button label  Each button should have a different label  Support display of Icons

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JButton 

Constructors Jbutton myButton = new JButton( "Button" ); Jbutton myButton = new JButton( "Button", myIcon );

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Method  setRolloverIcon( myIcon ) 

Sets image to display when mouse over button

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JCheckBox 

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State buttons  JToggleButton  Subclasses JCheckBox, JRadioButton  Have on/off (true/false) values  We discuss JCheckBox in this section Initialization  JCheckBox myBox = new JCheckBox( "Title" ); When JCheckBox changes  ItemEvent generated  Handled by an ItemListener, which must define itemStateChanged  Register with addItemListener 31

JCheckBox 

ItemEvent methods  getStateChange  Returns ItemEvent.SELECTED or ItemEvent.DESELECTED

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JComboBox 

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Combo box (drop down list)  List of items, user makes a selection  Class JComboBox  Generate ItemEvents JComboBox  Numeric index keeps track of elements  First element added at index 0  First item added is appears as currently selected item when combo box appears

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JComboBox 

Methods  getSelectedIndex  Returns the index of the currently selected item  setMaximumRowCount( n )  Set the maximum number of elements to display when user clicks combo box  Scrollbar automatically provided

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Mouse Event Handling 

Mouse events  Can be trapped for any GUI component derived from java.awt.Component  Mouse event handling methods  Take a MouseEvent object  Contains info about event, including x and y coordinates  Methods getX and getY  MouseListener and MouseMotionListener methods called automatically (if component is registered)  addMouseListener  addMouseMotionListener 35

Layout Managers 

Layout managers Arrange GUI components on a container  Provide basic layout capabilities 

 Easier

to use than determining exact size and position of every component  Programmer concentrates on "look and feel" rather than details

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FlowLayout 

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Most basic layout manager  Components placed left to right in order added  When edge of container reached, continues on next line  Components can be left-aligned, centered (default), or rightaligned Method  setAlignment  FlowLayout.LEFT, FlowLayout.CENTER, FlowLayout.RIGHT  layoutContainer( Container )  Update Container specified with layout 37

BorderLayout 

BorderLayout  Default manager for content pane  Arrange components into 5 regions  North, south, east, west, center  Up to 5 components can be added directly  One for each region  Components placed in  North/South - Region is as tall as component  East/West - Region is as wide as component  Center - Region expands to take all remaining space

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BorderLayout 

Methods  Constructor: BorderLayout( hGap, vGap );  hGap - horizontal gap space between regions  vGap - vertical gap space between regions  Default is 0 for both  Adding components  myLayout.add( component, position )  component - component to add  position - BorderLayout.NORTH 

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SOUTH, EAST, WEST, CENTER similar

setVisible( boolean ) ( in class Jbutton)  If false, hides component layoutContainer( container ) - updates container, as before

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GridLayout 

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GridLayout  Divides container into a grid  Components placed in rows and columns  All components have same width and height  Added starting from top left, then from left to right  When row full, continues on next row, left to right Constructors  GridLayout( rows, columns, hGap, vGap )  Specify number of rows and columns, and horizontal and vertical gaps between elements (in pixels)  GridLayout( rows, columns )  Default 0 for hGap and vGap 40

GridLayout 

Updating containers  Container method validate  Re-layouts a container for which the layout has changed  Example: Container c = getContentPane; c.setLayout( myLayout ); if ( x = 3 ){ c.setLayout( myLayout2 ); c.validate(); }  Changes layout and updates c if condition met 41

Panels 

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Complex GUIs  Each component needs to be placed in an exact location  Can use multiple panels  Each panel's components arranged in a specific layout Panels  Class JPanel inherits from JComponent, which inherits from java.awt.Container  Every JPanel is a Container  JPanels can have components (and other JPanels) added to them  JPanel sized to components it contains  Grows to accommodate components as they are added 42

Panels 

Usage  Create panels, and set the layout for each  Add components to the panels as needed  Add the panels to the content pane (default BorderLayout)

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Creating a Self-Contained Subclass of JPanel -1

JPanel 

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Can be used as a dedicated drawing area  Receive mouse events  Can extend to create new components Combining Swing GUI components and drawing can lead to improper display  GUI may cover drawing, or may be able to draw over GUI components Solution: separate the GUI and graphics  Create dedicated drawing areas as subclasses of JPanel

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Creating a Self-Contained Subclass of JPanel -2

Swing components inheriting from JComponent 

Contain method paintComponent Helps to draw properly in a Swing GUI When customizing a JPanel, override paintComponent public void paintComponent( Graphics g ) { super.paintComponent( g ); 



//additional drawing code } 

Call to superclass paintComponent ensures painting occurs in proper order  The call should be the first statement - otherwise, it will erase any drawings before it 45

Creating a Self-Contained Subclass of JPanel -3

JFrame and JApplet 

Not subclasses of JComponent  Do

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not contain paintComponent

Override paint to draw directly on subclasses

Events JPanels do not create events like buttons  Can recognize lower-level events 

 Mouse

and key events 46

Creating a Self-Contained Subclass of JPanel-4

Example  Create a subclass of JPanel named SelfContainedPanel that listens for its own mouse events  Draws an oval on itself (overrides paintComponent) 

Import SelfContainedPanel into another class

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The other class contains its own mouse handlers Add an instance of SelfContainedPanel to the content panel 

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Windows 

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JFrame  Inherits from java.awt.Frame, which inherits from java.awt.Window  JFrame is a window with a title bar and a border  Not a lightweight component - not written completely in Java  Window part of local platform's GUI components  Different for Windows, Macintosh, and UNIX JFrame operations when user closes window  Controlled with method setDefaultCloseOperation  Interface WindowConstants (javax.swing) has three constants to use 

DISPOSE_ON_CLOSE, DO_NOTHING_ON_CLOSE, HIDE_ON_CLOSE (default)

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Windows -2

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Windows take up valuable resources  Explicitly remove windows when not needed with method dispose (of class Window, indirect superclass of JFrame)  Or, use setDefaultCloseOperation  DO_NOTHING_ON_CLOSE - you determine what happens when user wants to close window Display  By default, window not displayed until method show called  Can display by calling method setVisible( true )  Method setSize - make sure to set a window's size, otherwise only the title bar will appear 49

Windows -3

All windows generate window events  addWindowListener  WindowListener interface has 7 methods  windowActivated  windowClosed (called after window closed)  windowClosing (called when user initiates closing)  windowDeactivated  windowIconified (minimized)  windowDeiconified  windowOpened

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Using Menus with Frames 

Menus   

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Important part of GUIs Perform actions without cluttering GUI Attached to objects of classes that have method setJMenuBar  JFrame and JApplet

Classes used to define menus  

JMenuBar - container for menus, manages menu bar JMenuItem - manages menu items  Menu items - GUI components inside a menu  Can initiate an action or be a submenu 51

Using Menus with Frames -2

Classes used to define menus (continued) 

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JMenu - manages menus  Menus contain menu items, and are added to menu bars  Can be added to other menus as submenus  When clicked, expands to show list of menu items JCheckBoxMenuItem  Manages menu items that can be toggled  When selected, check appears to left of item JRadioButtonMenuItem  Manages menu items that can be toggled  When multiple JRadioButtonMenuItems are part of a group, only one can be selected at a time  When selected, filled circle appears to left of item

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Using Menus with Frames -3

Mnemonics Provide quick access to menu items (File)  Can be used with classes that have subclass javax.swing.AbstractButton  Use method setMnemonic JMenu fileMenu = new JMenu( "File" ) fileMenu.setMnemonic( 'F' );  Press Alt + F to access menu Methods  setSelected( true )  Of class AbstractButton  Sets button/item to selected state 

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Using Menus with Frames -3

Methods (continued) 

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addSeparator()  Class JMenu  Inserts separator line into menu

Dialog boxes 

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Modal - No other window can be accessed while it is open (default)  Modeless - other windows can be accessed JOptionPane.showMessageDialog( parentWindow, String, title, messageType ) parentWindow - determines where dialog box appears  null - displayed at center of screen  window specified - dialog box centered horizontally over parent 54

Using Menus with Frames-4

Using menus 

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Create menu bar  Set menu bar for JFrame ( setJMenuBar( myBar ); ) Create menus  Set Mnemonics Create menu items  Set Mnemonics  Set event handlers If using JRadioButtonMenuItems  Create a group: myGroup = new ButtonGroup();  Add JRadioButtonMenuItems to the group 55

Using Menus with Frames-5

Using menus (continued) Add menu items to appropriate menus  myMenu.add( myItem );  Insert separators if necessary: myMenu.addSeparator();  If creating submenus, add submenu to menu  myMenu.add( mySubMenu );  Add menus to menu bar  myMenuBar.add( myMenu ); Example  Use menus to alter text in a JLabel  Change color, font, style  Have a "File" menu with a "About" and "Exit" items 

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